How do you fix the error: fix attempt to preform arithmetic (add) on instance and number?

Hello! I've been experiencing this error with NumberValues and IntValues, I was wondering if anyone can help I guess.

local BuyAndSellAmount = script.Parent
local number = math.random(1,6)

while true do
	wait(5)
	if number == 1 then
		
		local numb = 1
		
		print("+1")
		BuyAndSellAmount = BuyAndSellAmount + numb

		
	elseif number == 2 then
		
		local numb = 0.1
		
		print("+0.1")
		BuyAndSellAmount = BuyAndSellAmount + numb

	elseif number == 3 then
		
		local numb = 2
		
		print("+2")
		BuyAndSellAmount = BuyAndSellAmount + numb

	elseif number == 4 then
		
		local numb = 1
		
		print("-1")
		BuyAndSellAmount = BuyAndSellAmount - numb

	elseif number == 5 then
		
		local numb = 0.1
		
		print("-0.1")
		BuyAndSellAmount = BuyAndSellAmount - numb

	elseif number == 6 then
		
		local numb = 2
		
		print("-2")
		BuyAndSellAmount = BuyAndSellAmount - numb

    


	end	

Also note that im currenently trying to add/subtract 2 numbers every few seconds.

This is because numb is a number while Buy and sell amount is not a number and is an instance. You should use .Value to get the value of the instance. for example

 BuyAndSellAmount.Value = BuyAndSellAmount.Value - numb